Your cats metabolism before sterilisation is able to cope with a constant supply of energy and it would only eat only as much as is necessary to meet its energy demands after the sterilisation however your cats body loses the ability to regulate and it frequently eats more than it needs which can lead to weight gain older cats may also have age related issues such as less activity or renal problems as soon as 48 hours after sterilisation has taken place your cats ingestion can rise by 2